Conventional draining systems usually comprise a main pipe for each street or neighbourhood from which a large number of lateral pipes project. The lateral pipes service individual properties or groups of properties. The main pipe usually has a minimum inner diameter of the order of 6" or 150 mm and is fairly straight and readily accessible. Access to the main pipe is usually provided through manholes and the like in the street. The lateral pipes on the other hand are usually small (an inner diameter of the order of 4" or 100 mm), quite often have bends in them, quite often extend at angles to the horizontal, and are usually not accessible for testing without excavation. It is therefore very difficult to test for leaks in lateral pipes or in fact to test if they are in use or not. Moreover, in some drainage systems, difficulties arise in testing for leaks in the main pipe.
One apparatus for testing drainage systems that is known to the inventor is in use in the Auckland region in New Zealand. This apparatus comprises an elongate member that has an inflatable seal adjacent each end. In use this apparatus is dragged down the main pipe until it reaches the lateral pipe to be tested. The apparatus is then manipulated so that one seal is positioned on one side of the lateral pipe and the other seal is positioned on the other side of the lateral pipe. The seals are then inflated so that they tightly engage the inner diameter of the main pipe. In this way the entrance to the lateral pipe is sealed off. Water is then poured down the lateral pipe from some suitable access point. The amount of water poured down the lateral pipe is then monitored. If there is a leak in the lateral pipe, water must be added continually to keep the lateral pipe full. The fact that water needs to be added indicates that there is a leak and the amount of water added gives some indication of the size of the leak.
This apparatus goes some way towards solving the problem of detecting leaks in lateral pipes but has a number of problems. First it can only be used to test leaks in lateral pipes and only those for which some external access point is available. Hence inaccessible joints and faults cannot be tested. Secondly there is no guarantee that the leak is not caused by the inflatable seal not sealing properly against the inner diameter of the main pipe. Quite frequently debris and the like occurs in drainage systems and this can interfere witch the seal between the inflated seal and the inner diameter of the main pipe. Thirdly the apparatus cannot be readily automated. Fourthly, if the level of the access point to the lateral pipe is more than about 6 meters above the level of the main pipe, it cannot be filled with water because the hydrostatic pressure at the main pipe would exceed the maximum generally allowed in the relevant standard specifications.